Methods for biosynthesis of isoprene

ABSTRACT

This document describes biochemical pathways for producing isoprene by forming two vinyl groups in a central precursor produced from isobutyryl-CoA, 3-methyl-2-oxopentanoate, or 4-methyl-2-oxopentanoate as well as recombinant hosts for producing isoprene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No. 61/862,401, filed Aug. 5, 2013, the disclosure of which is incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to methods for biosynthesizing isoprene using one or more isolated enzymes such as one or more of a dehydratase, a monooxygenase, a cytochrome P450, an acyl-[acp] dehydrogenase, a mevalonate diphosphate decarboxylase, an acyl-[acp] decarboxylating thioesterase, and a mevalonate-3-kinase; or using recombinant host cells expressing one or more such enzymes.

BACKGROUND

Isoprene is an important monomer for the production of specialty elastomers including motor mounts/fittings, surgical gloves, rubber bands, golf balls and shoes. Styrene-isoprene-styrene block copolymers form a key component of hot-melt pressure-sensitive adhesive formulations and cis-poly-isoprene is utilised in the manufacture of tires (Whited et al., Industrial Biotechnology, 2010, 6(3), 152-163).

Manufacturers of rubber goods depend on either imported natural rubber from the Brazilian rubber tree or petroleum-based synthetic rubber polymers (Whited et al., 2010, supra).

Given a reliance on petrochemical feedstocks and the harvesting of trees, biotechnology offers an alternative approach via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds.

Accordingly, against this background, it is clear that there is a need for sustainable methods for producing intermediates, in particular isoprene, wherein the methods are biocatalysis based.

Both bioderived feedstocks and petrochemical feedstocks are viable starting materials for the biocatalysis processes.

The introduction of vinyl groups into medium carbon chain length enzyme substrates is a key consideration in synthesising isoprene via biocatalysis processes.

There are known metabolic pathways leading to the synthesis of isoprene in prokaryotes such as Bacillis subtillis and eukaryotes such as Populus alba (Whited et al., 2010, supra).

Isoprene may be synthesized via two routes leading to the precursor dimethylvinyl-PP, such as the mevalonate and the non-mevalonate pathway (Kuzuyama, Biosci. Biotechnol. Biochem., 2002, 66(8), 1619-1627). The mevalonate pathway incorporates a decarboxylase enzyme, mevalonate diphosphate decarboxylase (hereafter MDD), that introduces the first vinyl-group into the precursors leading to isoprene. The second vinyl-group is introduced by isoprene synthase (hereafter ISPS) in the final step in synthesizing isoprene.

The mevalonate pathway (FIG. 1) has been exploited in the biocatalytic production of isoprene using E. coli as host. E. coli engineered with the mevalonate pathway requires three moles of acetyl-CoA, three moles of ATP and two moles of NAD(P)H to produce a mole of isoprene. Given a theoretical maximum yield of 25.2% (w/w) for the mevalonate pathway, isoprene has been produced biocatalytically at a volumetric productivity of 2 g/(L·h) with a yield of 11% (w/w) from glucose (Whited et al., 2010, supra). Particularly, the phosphate activation of mevalonate to 5-diphosphomevalonate is energy intensive metabolically, requiring two moles of ATP per mole of isoprene synthesis (FIG. 1). Accordingly, reducing the ATP consumption can improve the efficiency of the pathway.

SUMMARY

The inventors have determined that it is possible to construct a biochemical pathway to synthesize isoprene from (R)-mevalonate, 3-methyl-2-oxopentanoate, 4-methyl-2-oxopentanoate or isobutyryl-CoA, by introducing two vinyl groups without the need for terminal alcohol phosphorylation. Such pathways rely on a dehydratase, monooxygenase, cytochrome P450, or dehydrogenase enzyme to introduce the first vinyl group; and a MDD, mevalonate-3-kinase, acyl-[acp] decarboxylating thioesterase (e.g., CurM TE) or a linalool dehydratase to introduce the second vinyl group into the precursors leading to isoprene synthesis. The methods described herein can include introducing the first vinyl group, introducing the second vinyl group, or introducing both the first and second vinyl groups.

Prior to the present invention, it was not known that enzymes capable of introducing two vinyl groups, without the need for terminal alcohol phosphorylation, could be used to generate non-phosphorylated intermediates for the synthesis of isoprene. Thus the invention provides enzymes that can convert the central precursors mevalonate, 3-methyl-2-oxopentanoate, 4-methyl-2-oxopentanoate or isobutyryl-CoA into isoprene.

In some embodiments, 3-methyl-pent-2-enoyl-CoA or 4-methyl-pent-2-enoyl-CoA is formed by a 2-hydroxyacyl-CoA dehydratase classified, for example, under EC 4.2.1.-, such as the gene products of HadBC (SEQ ID NOs: 3 and 4) and its initiator HadI (SEQ ID NO: 2), or the gene products of HgdAB (SEQ ID NOs: 6 and 7) and its initiator HdgC (SEQ ID NO: 5). In some embodiments, the 2-hydroxyacyl-CoA dehydratase is the result of enzyme engineering. The 2-hydroxyacyl-CoA dehydratase enzymes isolated from anaerobic bacteria possess a common catalytic mechanism employed in amino acid degradation pathways. For example, the gene products of HadBC/HadI from Clostridium difficile catalyse the conversion of (R)-2-hydroxyisocaproyl-CoA to isocaprenoyl-CoA. Similarly, the gene products of HgdAB/HdgC catalyse the conversion of 2-hydroxyglutaryl-CoA to glutaconyl-CoA (Kim et al., FEMS Microbiol. Reviews, 2004, 28, 455-468). See FIGS. 2-5.

In some embodiments, the first vinyl group is introduced into 3-methyl-pent-2-enoyl-ACP, derived from the central metabolite 3-methyl-2-oxopentanoate, which may be enzymatically converted in one or more steps to 3-methyl-3-hydroxypent-4-enoate or 3-methyl-3-sulphoryl-pent-4-enoyl-ACP (as shown, for example, in FIG. 2). It has been demonstrated that the gene product of tcsD (SEQ ID NO: 14) from Streptomyces kanamyceticus has dehydrogenase activity for straight and branch chain C5 acyl-ACP substrates (Mo et al., JACS, 2011, 133, 976-985).

In some embodiments, the first vinyl group is introduced forming 4-methyl-pent-2-enoyl-ACP, derived from the central metabolite 4-methyl-2-oxopentanoate or isobutyryl-CoA, which may be enzymatically converted in one or more steps to 4-methyl-3-hydroxypent-4-enoate, 4-methyl-3-sulphoryl-pent-4-enoyl-ACP, or 3-methyl-3-buten-2-ol (see, for example, FIG. 3, FIG. 6, and FIG. 7). It has been demonstrated that the gene product of tcsD (SEQ ID NO: 14) from Streptomyces kanamyceticus has dehydrogenase activity for 4-methyl-pent-2-enoyl-ACP (Mo et al., 2011, supra).

In some embodiments, the first vinyl group is introduced into 3-methyl-3-hydroxy-pentanoate, which may be enzymatically converted in one or more steps to 3-methyl-3-hydroxypent-4-enoate (see, for example, FIG. 4). It has been demonstrated that the monooxygenase encoded by mdpJ (SEQ ID NO: 15) introduces a terminal double bond into allyl groups bound to a secondary alcohol (Schäfer et al., Appl. Environ. Microbiol., 2012, 78(17), 6280-6284).

In some embodiments, the first vinyl group is introduced into 4-methyl-3-hydroxypentanoate, which may be enzymatically converted in one or more steps to 4-methyl-3-hydroxypent-4-enoate (see, for example, FIG. 5).

In some embodiments, the first vinyl group is introduced into mevalonate, which can be converted enzymatically in one or more steps to 3-hydroxy-3-methyl-pent-4-enoate (as shown, for example, in FIG. 8).

In some embodiments, the 3-hydroxy functional group is introduced into 3-methyl-pent-2-enoyl-CoA or 4-methyl-pent-2-enoyl-CoA by a (R)-specific enoyl-CoA hydratase enzyme classified, for example, under EC 4.2.1.119 such as the gene product of phaJ (SEQ ID NO: 16, Fukui et al., J. Bacteriol., 1998, 180(3), 667-673) or MaoC (SEQ ID NO: 17; Park and Lee, J. Bacteriol., 2003, 185(18), 5291-5397) or a bacterial (S)-specific enoyl-CoA hydratase classified, for example, under EC 4.2.1.17 such as the gene product of YsiB (SEQ ID NO: 1). In some embodiments, the enoyl-CoA hydratase enzyme is the result of enzyme engineering. A single enzyme candidate for the introduction of a 3-hydroxy functional group into 3-methylbuten-2-enoyl-CoA has been identified previously in the cell free extract of Galactomyces reessii, containing an enoyl-CoA hydratase classified in EC 4.2.1.17 that converts 3-methylbuten-2-enoyl-CoA to 3-hydroxy-3-methylbutanoyl-CoA (Lee et al., Appl. Environ. Microbiol., 1997, 63(11), 4191-4195). Equivalent enoyl-CoA hydratase activity from bacterial origin has not been identified. See FIG. 4 and FIG. 5.

In some embodiments, 4-methyl-3-oxopentanoyl-ACP is formed by condensing isobutyryl-CoA and malonyl-ACP using a β-ketoacyl-ACP-synthase enzyme classified, for example, under EC 2.3.1.- (EC 2.3.1.41,EC 2.3.1.79, or EC 2.3.1.80) such as the gene product of AnlF (SEQ ID NO: 18). It has been demonstrated that the gene product of anlF condenses isobutyryl-CoA and malonyl-ACP (Lechner et al., ACS Synth. Biol., 2013, 2(7), 379-83).

In some embodiments, the second vinyl group is introduced into a medium chain carbon alkenoate by a mevalonate diphosphate decarboxylase (Lefurgy et al., J. Biol. Chem., 2010, 285(27), 20654-20663) or a mevalonate 3-kinase (Vinokur et al., Biochemistry, 2014, 53(25), 4161-4168), converting 3-methyl-3-hydroxypent-4-enoate or 4-methyl-3-hydroxypent-4-enoate to isoprene (FIGS. 2-5).

In some embodiments, the second vinyl group is introduced into a medium chain carbon alkenoate by a decarboxylating thioesterase (CurM TE), converting 3-methyl-3-sulphoryl-pent-4-enoyl-ACP or 4-methyl-3-sulphoryl-pent-4-enoyl-ACP to isoprene (see, FIG. 2, FIG. 3 and FIG. 6; Gehret et al., J. Biol. Chem., 2011, 286(16), 14445-14454).

In some embodiments, the second vinyl group is introduced by a linalool dehydratase classified, for example, under EC 4.2.1.127 (Brodkorb et al., J. Biol. Chem., 2010, 285(40), 30436-30442) or a dehydratase classified under EC 4.2.1.- (such as one isolated from species such as Aquincola tertiaricarbonis or Methylibium petroleiphilum PM1; Schäfer et al., 2011, supra) (FIG. 3 and FIG. 7).

In one aspect, this document features a method for enzymatically synthesizing isoprene. The method includes enzymatically introducing a terminal vinyl group into 3-methyl-pent-2-enoyl-[acp], 4-methyl-pent-2-enoyl-[acp], 3-methyl-3-hydroxy-pentanoate, 4-methyl-3-hydroxypentanoate, or mevalonate, and converting the resulting product in one or more steps to isoprene. The first vinyl group can be introduced using a dehydratase classified under EC 4.2.1.- (e.g., a dehydratase having at least 70% homology to the amino acid sequence set forth in SEQ ID NO: 22), a monooxygenase (e.g., a monooxygenase having at least 70% homology to the amino acid sequence set forth in SEQ ID NO: 15), a cytochrome P450 reductase, or an acyl-[acp] dehydrogenase (e.g., an acyl-[acp] dehydrogenase having at least 70% homology to the amino acid sequence set forth in SEQ ID NO:14). For example, a terminal vinyl group can be introduced into 3-methyl-pent-2-enoyl-[acp] or 4-methyl-pent-2-enoyl-[acp] using an acyl-[acp] dehydrogenase. For example, a terminal vinyl group can be introduced into mevalonate using a dehydratase classified under EC 4.2.1.-. For example, a terminal vinyl group can be introduced into 3-methyl-3-hydroxy-pentanoate or 4-methyl-3-hydroxypentanoate using a monooxygenase or a cytochrome P450 reductase. 3-methyl-pent-2-enoyl-[acp], 4-methyl-pent-2-enoyl-[acp], 3-methyl-3-hydroxy-pentanoate, or 4-methyl-3-hydroxypentanoate, can be enzymatically formed from 3-methyl-2-oxopentanoate, 4-methyl-2-oxopentanoate, or isobutyryl-CoA.

This document also features a method for enzymatically synthesizing isoprene that includes enzymatically introducing a second terminal vinyl group into 3-methyl-3-hydroxy-pent-4-enoate, 4-methyl-3-hydroxypent-4-enoate, 4-methyl-3-sulphorylpent-4-enoyl-[acp], or 3-methyl-3-buten-2-ol to produce isoprene. The second vinyl group can be introduced using a mevalonate diphosphate decarboxylase, a mevalonate 3-kinase, an acyl-[acp] decarboxylating thioesterase, or a linalool dehydratase. The mevalonate diphosphate decarboxylase can have at least 70% homology to the mevalonate diphosphate decarboxylase of any one of the amino acid sequences set forth in SEQ ID NOs:8-11. The mevalonate 3-kinase can have at least 70% homology to the amino acid sequence of SEQ ID NO: 12. The acyl-[acp] decarboxylating thioesterase can have at least 70% homology to the amino acid sequence of SEQ ID NO: 21. The linalool dehydratase can have at least 70% homology to the amino acid sequence of SEQ ID NO: 13. The mevalonate diphosphate decarboxylase can have a histidine at the position aligning with residue 74 of SEQ ID NO:11 and/or a phenylalanine at the position aligning with residue 145 of SEQ ID NO:11. The mevalonate diphosphate decarboxylase can have the amino acid sequence set forth in SEQ ID NO:11, except that a histidine is substituted at position 74 for arginine and/or a phenylalanine is substituted at position 145 for isoleucine. For example, the mevalonate diphosphate decarboxylase can convert 3-methyl-3-hydroxypent-4-enoate or 4-methyl-3-hydroxypent-4-enoate to isoprene. For example, a mevalonate 3-kinase can convert 3-methyl-3-hydroxypent-4-enoate or 4-methyl-3-hydroxypent-4-enoate to isoprene. For example, the acyl-[acp] decarboxylating thioesterase can convert 3-methyl-3-sulphorylpent-4-enoyl-[acp] or 4-methyl-3-sulphorylpent-4-enoyl-[acp] to isoprene. For example, the linalool dehydratase can convert 3-methyl-3-buten-2-ol to isoprene.

Any of the methods described herein can be performed using isolated enzymes.

Any of the methods described herein can be performed using cell lysates comprising the enzymes.

Any of the methods described herein can be performed in a recombinant host. For example, the host can be a prokaryote selected from the group consisting of the genus Escherichia such as Escherichia coli; from the genus Clostridia such as Clostridium ljungdahlii, Clostridium autoethanogenum or Clostridium kluyveri; from the genus Corynebacteria such as Corynebacterium glutamicum; from the genus Cupriavidus such as Cupriavidus necator or Cupriavidus metallidurans; from the genus Pseudomonas such as Pseudomonas fluorescens or Pseudomonas putida; from the genus Bacillus such as Bacillus subtillis; or from the genus Rhodococcus such as Rhodococcus equi. The host can be a eukaryote selected from the group consisting of the genus Aspergillus such as Aspergillus niger; from the genus Saccharomyces such as Saccharomyces cerevisiae; from the genus Pichia such as Pichia pastoris; from the genus Yarrowia such as Yarrowia lipolytica, from the genus Issatchenkia such as Issathenkia orientalis; from the genus Debaryomyces such as Debaryomyces hansenii; from the genus Arxula such as Arxula adenoinivorans; or from the genus Kluyveromyces such as Kluyveromyces lactis.

The host can be subjected to a fermentation strategy entailing anaerobic, micro-aerobic or aerobic cultivation. A cell retention strategy using a ceramic hollow fiber membrane can be employed to achieve and maintain a high cell density during fermentation.

The principal carbon source fed to the fermentation can derive from a biological or a non-biological feedstock. The biological feedstock can be, or can derive from, monosaccharides, disaccharides, hemicellulose such as levulinic acid and furfural, cellulose, lignocellulose, lignin, triglycerides such as glycerol and fatty acids, agricultural waste or municipal waste. The non-biological feedstock can be, or can derive from, either natural gas, syngas, CO₂/H₂, methanol, ethanol, non-volatile residue (NVR), caustic wash from cyclohexane oxidation processes or other waste stream from either the chemical or petrochemical industries.

This document also features a recombinant host producing isoprene. The host includes at least one exogenous nucleic acid encoding (i) a 2-hydroxyacyl-CoA dehydratase or a β-ketoacyl-ACP-synthase; (ii) an acyl-ACP dehydrogenase, a monooxygenase, a cytochrome P450, or a dehydratase classified under EC 4.2.1.- and (iii) a mevalonate diphosphate decarboxylase, a mevalonate 3-kinase, an acyl-ACP decarboxylating thioesterase, or a linalool dehydratase, the host producing isoprene. The host can include at least one exogenous nucleic acid encoding (i) the 2-hydroxyacyl-CoA dehydratase, (ii) the acyl-ACP dehydrogenase, and (iii) the mevalonate diphosphate decarboxylase, mevalonate 3-kinase, acyl-ACP decarboxylating thioesterase, or linalool dehydratase. The host can include at least one exogenous nucleic acid encoding (i) the 2-hydroxyacyl-CoA dehydratase, (ii) the monooxygenase or cytochrome P450, and (iii) the mevalonate diphosphate decarboxylase, mevalonate 3-kinase, acyl-ACP decarboxylating thioesterase, or linalool dehydratase. The host can include at least one exogenous nucleic acid encoding (i) the β-ketoacyl-ACP-synthase, (ii) the acyl-ACP dehydrogenase, and (iii) the mevalonate diphosphate decarboxylase, mevalonate 3-kinase, acyl-ACP decarboxylating thioesterase, or linalool dehydratase.

This document also features a recombinant host that includes at least one exogenous nucleic acid encoding (i) a dehydratase classified under EC 4.2.1.- and (ii) a mevalonate diphosphate decarboxylase or a mevalonate 3-kinase, the host producing isoprene.

In any of the recombinant hosts, the enzymes from the mevalonate pathway leading to isoprenoid synthesis, such as enzymes classified under EC 2.3.1.9, EC 2.3.3.10, EC 1.1.1.34 or EC 1.1.1.88, can be introduced or gene dosed into the host that utilizes the non-mevalonate or 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid synthesis.

In the recombinant host, the enzymes from the non-mevalonate or 2-C-methyl-D-erythritol 4-phosphate pathway can be introduced into a host microorganism that utilizes the mevalonate pathway for isoprenoid synthesis.

In any of the recombinant hosts described herein, the host can include one or more of the following attenuated enzymes: the enzyme classified under EC 2.7.1.36 accepting mevalonate as substrate, a polymer synthase, an acetate kinase, a lactate dehydrogenase, an enzyme degrading phosphoenolpyruvate to succinate, and an enzyme degrading acetyl-CoA to ethanol.

In any of the recombinant hosts described herein, the host can overexpress one or more genes encoding: an enzyme for 3′-phosphoadenosine-5′-phosphosulfate synthesis, a puridine nucleotide transhydrogenase, a glyceraldehyde-3-phosphate-dehydrogenase, a malic enzyme, a glucose-6-phosphate dehydrogenase, and a fructose 1,6-diphosphatase.

In any of the recombinant hosts described herein, the host can include a feedback inhibition resistant mutant of an acetolactate synthase.

In any of the recombinant hosts described herein, the host can include an acetolactate synthase under control of a promoter not subject to genetic repression by a branched chain amino acid.

The reactions of the pathways described herein can be performed in one or more cell (e.g., host cell) strains (a) naturally expressing one or more relevant enzymes, (b) genetically engineered to express one or more relevant enzymes, or (c) naturally expressing one or more relevant enzymes and genetically engineered to express one or more relevant enzymes. Alternatively, relevant enzymes can be extracted from any of the above types of host cells and used in a purified or semi-purified form. Extracted enzymes can optionally be immobilized to a solid substrate such as the floors and/or walls of appropriate reaction vessels. Moreover, such extracts include lysates (e.g., cell lysates) that can be used as sources of relevant enzymes. In the methods provided by the document, all the steps can be performed in cells (e.g., host cells), all the steps can be performed using extracted enzymes, or some of the steps can be performed in cells and others can be performed using extracted enzymes.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and the drawings, and from the claims. The word “comprising” in the claims may be replaced by “consisting essentially of” or with “consisting of,” according to standard practice in patent law.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of an exemplary biochemical pathway leading to isoprene using (R)-mevalonate as a central precursor via isopentenyl diphosphate and dimethyl allyl diphosphate.

FIG. 2 is a schematic of exemplary biochemical pathways leading to isoprene using 3-methyl-2-oxopentanoate as a central precursor and an acyl-ACP dehydrogenase.

FIG. 3 is a schematic of exemplary biochemical pathways leading to isoprene using 4-methyl-2-oxopentanoate as a central precursor and an acyl-ACP dehydrogenase.

FIG. 4 is a schematic of an exemplary biochemical pathway leading to isoprene using 3-methyl-2-oxopentanoate as a central precursor and a monooxygenase.

FIG. 5 is a schematic of an exemplary biochemical pathway leading to isoprene using 4-methyl-2-oxopentanoate as a central precursor and a monooxygenase.

FIG. 6 is a schematic of exemplary biochemical pathways leading to isoprene using isobutyryl-CoA as a central precursor and an acyl-ACP dehydrogenase to introduce the first vinyl group and a GHMP superfamily enzyme to introduce the second vinyl group.

FIG. 7 is a schematic of exemplary biochemical pathways leading to isoprene using isobutyryl-CoA as a central precursor and an acyl-ACP dehydrogenase to introduce the first vinyl group and a dehydratase, such as linalool dehydratase, to introduce the second vinyl group.

FIG. 8 is a schematic of an exemplary biochemical pathway leading to isoprene using (R)-mevalonate as a central precursor via 3-hydroxy-3-methyl-pent-4-enoate.

FIGS. 9A-9F contain the amino acid sequences of a Bacillus subtilis enoyl-CoA hydratase encoded by YsiB (see Genbank Accession No. CAA99573.1, SEQ ID NO:1), a Clostridium difficile 2-hydroxyacyl-CoA dehydratase activator encoded by HadI (See Genbank Accession No. AAV40818.1, SEQ ID NO: 2), a Clostridium difficile 2-hydroxyacyl-CoA dehydratase encoded by HadBC (see Genbank Accession Nos. AAV40819.1 and AAV40820.1, SEQ ID NO: 3 and SEQ ID NO:4, respectively), an Acidaminococcus fermentans 2-hydroxyacyl-CoA dehydratase activator encoded by HgdC (See Genbank Accession No. CAA42196.1, SEQ ID NO: 5), an Acidaminococcus fermentans 2-hydroxyacyl-CoA dehydratase encoded by HdgAB (see Genbank Accession Nos. CAA32465.1 and CAA32466.1, SEQ ID NO: 6 and SEQ ID NO:7, respectively), a Streptococcus pyogenes mevalonate diphosphate decarboxylase (see Genbank Accession No. AAK33797.1, SEQ ID NO: 8), a Thioalkalimicrobium aerophilum mevalonate diphosphate decarboxylase (see Genbank Accession No. AHF01884.1, SEQ ID NO: 9), a Streptococcus pneumoniae mevalonate diphosphate decarboxylase (see Genbank Accession No. CAR68209.1, SEQ ID NO: 10), a Saccharomyces cerevisiae mevalonate diphosphate decarboxylase (see Genbank Accession No. CAA66158.1, SEQ ID NO: 11), a Thermoplasma acidophilum mevalonate 3-kinase (see Genbank Accession No. CAC12426.1, SEQ ID NO: 12), a Castellaniella defragrans linalool dehydratase (see Genbank Accession No. CBW30776.1, SEQ ID NO: 13), a Streptomyces kanamyceticus acyl-ACP dehydrogenase encoded by tcsD (see Genbank Accession No. ADU56239.1, SEQ ID NO: 14), an Aquincola tertiaricarbonis monooxygenase encoded by mdpJ (see Genbank Accession No. AER12131.1, SEQ ID NO: 15), an Aeromonas punctata enoyl-CoA hydratase encoded by phaJ (see Genbank Accession No. BAA21816.1, SEQ ID NO: 16), an Escherichia coli enoyl-CoA hydratase encoded by MaoC (see Genbank Accession No. AFY98994.1, SEQ ID NO: 17), a Streptomyces sp. CNH189 β-ketoacyl-ACP-synthase encoded by AnlF (see Genbank Accession No. AFY98994.1, SEQ ID NO: 18), a Synechococcus PCC 7002 sulfotransferase domain encoded by OLS ST (see Genbank Accession No. ACA99172.1, SEQ ID NO: 19), a Moorea producens 19L sulfotransferase domain encoded by CurM ST (see Genbank Accession No. ACV42478.1, SEQ ID NO: 20), a Moorea producens 19L thioesterase domain encoded by CurM TE (see Genbank Accession No. ACV42478.1, SEQ ID NO: 21) and an Elizabethkingia meningoseptica oleate hydratase enoded by ohyA (see Genbank Accession No. ACT54545.1, SEQ ID NO: 22).

FIG. 10 is a graph of the results from a spectrophotometric enzyme assay for enoyl-CoA hydratase (encoded by phaJ) activity in the forward direction, accepting crotonyl-CoA as substrate.

FIG. 11 is a table providing the details of an LC-MS analysis of an enzyme assay for enoyl-CoA hydratase (encoded by phaJ) activity in the reverse direction, accepting racemic 3-hydroxybutanoyl-CoA as substrate.

FIG. 12 is a table providing details of an LC-MS analysis of an enzyme assay for enoyl-CoA hydratase (encoded by phaJ) activity in the reverse direction, accepting 3-methyl-3-hydroxypentanoyl-CoA as substrate.

FIG. 13 is a table providing details of an LC-MS analysis of an enzyme assay for enoyl-CoA hydratase (encoded by phaJ) activity in the reverse direction, accepting 4-methyl-3-hydroxypentanoyl-CoA as substrate.

FIG. 14 is a bar graph of the logarithmic GC-MS species abundance for GHMP superfamily enzymes (AAK33797.1, SEQ ID NO: 8; AHF01884.1, SEQ ID NO: 9; CAR68209.1, SEQ ID NO: 10; CAA66158.1, SEQ ID NO: 11; CAA66158.1 having a histidine at position 74 instead of arginine; CAA66158.1 having a histidine at position 74 instead of arginine and a phenylalanine at position 145 instead of isoleucine; CAC12426.1, SEQ ID NO: 12) converting 3-methyl-3-hydroxypent-4-enoate to isoprene relative to the empty vector control.

FIG. 15 is a bar graph of the GC-MS peak area for linalool dehydratase (CBW30776.1, SEQ ID NO: 13) converting 3-methyl-3-buten-2-ol to isoprene relative to the empty vector control.

DETAILED DESCRIPTION

In particular, the invention provides enzymes and recombinant host microorganisms for isoprene synthesis in which two vinyl groups are introduced into central precursors such as 3-methyl-pent-2-enoyl-[acp], 4-methyl-pent-2-enoyl-[acp], 3-methyl-3-hydroxy-pentanoate, 4-methyl-3-hydroxypentanoate, or mevalonate, to produce isoprene in one or more enzymatic steps. 3-methyl-pent-2-enoyl-[acp], 4-methyl-pent-2-enoyl-[acp], 3-methyl-3-hydroxy-pentanoate, 4-methyl-3-hydroxypentanoate can be enzymatically produced from 3-methyl-2-oxopentanoate, 4-methyl-2-oxopentanoate, or isobutyryl-CoA, in one or more enzymatic steps. As used herein, the term “central precursor” is used to denote any metabolite in any metabolic pathway shown herein leading to the synthesis of isoprene. The term “central metabolite” is used herein to denote a metabolite that is produced in all microorganisms to support growth.

As such, host microorganisms described herein can include pathways that can be manipulated such that isoprene can be produced. In an endogenous pathway, the host microorganism naturally expresses all of the enzymes catalyzing the reactions within the pathway. A host microorganism containing an engineered pathway does not naturally express all of the enzymes catalyzing the reactions within the pathway but has been engineered such that all of the enzymes within the pathway are expressed in the host.

The term “exogenous” as used herein with reference to a nucleic acid (or a protein) and a host refers to a nucleic acid that does not occur in (and cannot be obtained from) a cell of that particular type as it is found in nature or a protein encoded by such a nucleic acid. Thus, a non-naturally-occurring nucleic acid is considered to be exogenous to a host once in the host. It is important to note that non-naturally-occurring nucleic acids can contain nucleic acid subsequences or fragments of nucleic acid sequences that are found in nature provided the nucleic acid as a whole does not exist in nature. For example, a nucleic acid molecule containing a genomic DNA sequence within an expression vector is non-naturally-occurring nucleic acid, and thus is exogenous to a host cell once introduced into the host, since that nucleic acid molecule as a whole (genomic DNA plus vector DNA) does not exist in nature. Thus, any vector, autonomously replicating plasmid, or virus (e.g., retrovirus, adenovirus, or herpes virus) that as a whole does not exist in nature is considered to be non-naturally-occurring nucleic acid. It follows that genomic DNA fragments produced by PCR or restriction endonuclease treatment as well as cDNAs are considered to be non-naturally-occurring nucleic acid since they exist as separate molecules not found in nature. It also follows that any nucleic acid containing a promoter sequence and polypeptide-encoding sequence (e.g., cDNA or genomic DNA) in an arrangement not found in nature is non-naturally-occurring nucleic acid. A nucleic acid that is naturally-occurring can be exogenous to a particular host microorganism. For example, an entire chromosome isolated from a cell of yeast x is an exogenous nucleic acid with respect to a cell of yeast y once that chromosome is introduced into a cell of yeast y.

In contrast, the term “endogenous” as used herein with reference to a nucleic acid (e.g., a gene) (or a protein) and a host refers to a nucleic acid (or protein) that does occur in (and can be obtained from) that particular host as it is found in nature. Moreover, a cell “endogenously expressing” a nucleic acid (or protein) expresses that nucleic acid (or protein) as does a host of the same particular type as it is found in nature. Moreover, a host “endogenously producing” or that “endogenously produces” a nucleic acid, protein, or other compound produces that nucleic acid, protein, or compound as does a host of the same particular type as it is found in nature.

For example, depending on the host and the compounds produced by the host, one or more of the following enzymes may be expressed in the host: 2-hydroxyacyl-CoA dehydratase, a 3-hydroxyacyl-[acp] dehydratase, a (R)-2-hydroxyacyl dehydrogenase, an acyl-ACP dehydrogenase such as the gene product of tcsD, a monooxgyenase such as the gene product of mdpJ, a (R)-specific enoyl-CoA hydratase such as the gene product of pha or MaoC, a (S)-specific enoyl-CoA hydratase such as the gene product of YsiB, a β-ketoacyl-ACP synthase such as the gene product of AnlF, a mevalonate diphosphate decarboxylase, a mevalonate 3-kinase, a decarboxylating thioesterase, a dehydratase, a linalool dehydratase, an oleate hydratase such as the gene product of ohyA, a kevitone hydrase, a carotenoid 1,2-hydratase, a CoA transferase, a CoA ligase, an acyl transferase, a thioesterase, an acyl[acp] thioesterase, a 3-hydroxyacyl-[acp]: CoA transacylase, a sulfotransferase, an acetoacetate decarboxylase, a secondary alcohol dehydrogenase, a hydroxymethylglutaryl-CoA reductase, a hydroxymethylglutaryl-CoA synthase, or a 3-oxoacyl-[acp] reductase.

In some embodiments, a recombinant host includes at least one exogenous nucleic acid encoding (i) a 2-hydroxyacyl-CoA dehydratase or a β-ketoacyl-ACP-synthase; (ii) an acyl-ACP dehydrogenase, a monooxygenase, a cytochrome P450, or a dehydratase classified under EC 4.2.1.- and (iii) a mevalonate diphosphate decarboxylase, a mevalonate 3-kinase, an acyl-ACP decarboxylating thioesterase, or a linalool dehydratase, and produces isoprene. For example, a host can include at least one exogenous nucleic acid encoding a 2-hydroxyacyl-CoA dehydratase, an acyl-ACP dehydrogenase, and a mevalonate diphosphate decarboxylase, a mevalonate 3-kinase, an acyl-ACP decarboxylating thioesterase, or a linalool dehydratase. For example, a host can include at least one exogenous nucleic acid encoding (i) a 2-hydroxyacyl-CoA dehydratase, (ii) a monooxygenase or a cytochrome P450, and (iii) a mevalonate diphosphate decarboxylase, mevalonate 3-kinase, acyl-ACP decarboxylating thioesterase, or linalool dehydratase. For example, a host can include at least one exogenous nucleic acid encoding (i) a β-ketoacyl-ACP-synthase, (ii) an acyl-ACP dehydrogenase, and (iii) a mevalonate diphosphate decarboxylase, mevalonate 3-kinase, acyl-ACP decarboxylating thioesterase, or linalool dehydratase.

In some embodiments, a recombinant host can include at least one exogenous nucleic acid encoding a (R)-2-hydroxyacyl dehydrogenase, a 2-hydroxyacyl-CoA dehydratase and 2-hydroxyacyl-CoA dehydratase initiator, and an acyl-[acp] dehydrogenase and produce 3-methyl-pent-2,4-dienoyl-[acp] or 4-methyl-pent-2,4-dienoyl-[acp]. Such a host also can include one or more of the following exogenous enzymes: a CoA transferase or a CoA ligase, and/or an acyl transferase and a 4′ phosphopantetheinyl transferase, and produce 3-methyl-pent-2,4-dienoyl-[acp] or 4-methyl-pent-2,4-dienoyl-[acp]. Either of such hosts further can include an exogenous 3-hydroxyacyl-[acp] dehydratase and further produce 3-methyl-3-hydroxypent-4-enoyl-[acp] or 4-methyl-3-hydroxypent-4-enoyl-[acp]. See, FIGS. 2 and 3.

In some embodiments, a recombinant host can include an exogenous nucleic acid encoding one or more of a β-ketoacyl-ACP-synthase and produce 4-methyl-3-hydroxypent-4-enoyl-[acp]. Such a host also can include one or more of the following exogenous enzymes: a 3-oxoacyl-[acp] reductase, a 3-hydroxyacyl-[acp] dehydratase, and an acyl-CoA dehydrogenase and produce 4-methyl-3-hydroxypent-4-enoyl-[acp]. See, FIG. 6 and FIG. 7.

In some embodiments, a recombinant host producing 3-methyl-3-hydroxypent-4-enoyl-[acp] or 4-methyl-3-hydroxypent-4-enoyl-[acp] further can include an exogenous sulfotransferase and an exogenous decarboxylating thioesterase and produce isoprene. See, FIG. 2, FIG. 3, and FIG. 6.

In some embodiments, a recombinant host producing 3-methyl-3-hydroxypent-4-enoyl-[acp] or 4-methyl-3-hydroxypent-4-enoyl-[acp] can include one or more of an exogenous (R)-3-hydroxyacyl-ACP:CoA transacylase, and a mevalonate diphosphate decarboxylase or a mevalonate 3-kinase and produce isoprene. Such a host also can include a thioesterase or a CoA transferase, and produce isoprene. See, FIG. 2, FIG. 3, and FIG. 6.

In some embodiments, a recombinant host producing 3-methyl-3-hydroxypent-4-enoyl-[acp] or 4-methyl-3-hydroxypent-4-enoyl-[acp] further can include one or more of an exogenous thioesterase (e.g., an acyl [acp] thioesterase) and a mevalonate diphosphate decarboxylase or a mevalonate 3-kinase and produce isoprene. See, FIG. 2, FIG. 3, and FIG. 6.

In some embodiments, a recombinant host producing 4-methyl-3-hydroxypent-4-enoyl-[acp] can include one or more of an exogenous (R)-3-hydroxyacyl-ACP: CoA transacylase, an acetoacetate decarboxylase, a secondary alcohol dehydrogenase, and a linalool dehydratase and produce isoprene. Such a host also can include one or more of the following exogenous enzymes: a dehydrogenase, a CoA-transferase, and/or a thioesterase and produce isoprene. See, FIG. 3 and FIG. 7.

In some embodiments, a recombinant host producing 4-methyl-3-hydroxypent-4-enoyl-[acp] can include one or more of an exogenous a thioesterase (e.g., an acyl-[acp] thioesterase), an acetoacetate decarboxylase, a secondary alcohol dehydrogenase, and a linalool dehydratase and produce isoprene. Such a host also can include an exogenous 3-oxoacyl-[acp] reductase and produce isoprene. See, FIG. 7.

In some embodiments, a recombinant host can include at least one exogenous nucleic acid encoding a (R)-2-hydroxyacyl dehydrogenase, a 2-hydroxyacyl-CoA dehydratase and 2-hydroxyacyl-CoA dehydratase initiator, and an (R)-specific or (S)-specific enoyl-CoA hydratase and produce 3-methyl-3-hydroxy-pentanoyl-CoA or 4-methyl-3-hydroxy-pentanoyl-CoA. Such a host also can include one or more of the following exogenous enzymes: a CoA transferase or a CoA ligase, and/or an acyl transferase and a 4′ phosphopantetheinyl transferase, and produce 3-methyl-3-hydroxy-pentanoyl-CoA or 4-methyl-3-hydroxy-pentanoyl-CoA. Such hosts further can include an exogenous thioesterase or a CoA transferase and further produce 3-methyl-3-hydroxypentanoate or 4-methyl-3-hydroxypentanoate. Any of such hosts further can include a monooxygenase and produce 3-methyl-3-hydroxy-pent-4-enoate or 4-methyl-3-hydroxypent-4-enoate. See, FIG. 4 and FIG. 5.

A recombinant host producing 3-methyl-3-hydroxy-pent-4-enoate or 4-methyl-3-hydroxypent-4-enoate can include a mevalonate diphosphate decarboxylase or a mevalonate 3-kinase and produce isoprene. See, FIG. 4 and FIG. 5.

In some embodiments, a recombinant host can include an exogneous dehydratase, and a mevalonate diphosphate decarboxylase or a mevalonate 3-kinase and produce isoprene. Such a host further can include one or more of the following exogenous enzymes: an acetyl-CoA C-acetyltransferase, a hydroxymethylglutaryl-CoA synthase, and/or a hydroxymethylglutaryl-CoA reductase, See, FIG. 8.

Within an engineered pathway, the enzymes can be from a single source, i.e., from one species, or can be from multiple sources, i.e., different species. Nucleic acids encoding the enzymes described herein have been identified from various organisms and are readily available in publicly available databases such as GenBank or EMBL.

Any of the enzymes described herein that can be used for isoprene production can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of the corresponding wild-type enzyme.

For example, an enoyl-CoA hydratase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Bacillus subtilis (GenBank Accession No. CAA99573.1, SEQ ID NO:1), a Aeromonas punctata (Genbank Accession No. BAA21816.1, SEQ ID NO: 16), or an Escherichia coli (Genbank Accession No. AFY98994.1, SEQ ID NO: 17) enoyl-CoA hydratase. See, FIG. 9.

For example, a 2-hydroxyacyl-CoA dehydratase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Clostridium difficile 2-hydroxyacyl-CoA dehydratase encoded by HadBC (Genbank Accession Nos. AAV40819.1 and AAV40820.1, SEQ ID NO: 3 and SEQ ID NO:4, respectively) or an Acidaminococcus fermentans 2-hydroxyacyl-CoA dehydratase encoded by HdgAB (Genbank Accession Nos. CAA32465.1 and CAA32466.1, SEQ ID NO: 6 and SEQ ID NO:7, respectively). See, FIG. 9.

A 2-hydroxyacyl-CoA dehydratase activator described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Clostridium difficile (Genbank Accession No. AAV40818.1, SEQ ID NO: 2) or an Acidaminococcus fermentans (Genbank Accession No. CAA42196.1, SEQ ID NO: 5) 2-hydroxyacyl-CoA dehydratase activator. See, FIG. 9.

For example, a mevalonate diphosphate decarboxylase (MDD) described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Streptococcus pyogenes (Genbank Accession No. AAK33797.1, SEQ ID NO: 8), Thioalkalimicrobium aerophilum (Genbank Accession No. AHF01884.1, SEQ ID NO: 9), Saccharomyces cerevisiae (GenBank Accession No. CAA66158.1, SEQ ID NO:11), or Streptococcus pneumonia (GenBank Accession No. CAR68209.1, SEQ ID NO:10). See, FIG. 9.

For example, a mevalonate 3-kinase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Thermoplasma acidophilum (Genbank Accession No. CAC12426.1, SEQ ID NO: 12) mevalonate 3-kinase. See, FIG. 9.

For example, a dehydratase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of the linalool dehydratase from Castellaniella defragrans (GenBank Accession No. CBW30776.1, SEQ ID NO:13). See FIG. 9.

For example, an acyl-ACP dehydrogenase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of the acyl-CoA dehydrogenase from Streptomyces kanamyceticus (encoded by the tcsD gene) (GenBank Accession No. ADU56239.1, SEQ ID NO: 14). See, FIG. 9.

For example, a monooxygenase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of an Aquincola tertiaricarbonis monooxygenase encoded by mdpJ (Genbank Accession No. AER12131.1, SEQ ID NO: 15). See, FIG. 9.

For example, a β-ketoacyl-ACP synthase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Streptomyces sp. CNH189 (Genbank Accession No. AFY98994.1, SEQ ID NO: 18) β-ketoacyl-ACP-synthase. See, FIG. 9.

For example, a sulfotransferase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Synechococcus PCC 7002 (Genbank Accession No. ACA99172.1, SEQ ID NO: 19) or Moorea producens 19L (Genbank Accession No. ACV42478.1, SEQ ID NO: 20) sulfotransferase. See, FIG. 9.

For example, a decarboxylating thioesterase described herein can have at least 70% sequence identity (homology) (e.g., at least 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or 100%) to the amino acid sequence of a Moorea producens 19L (Genbank Accession No. ACV42478.1, SEQ ID NO: 21) decarboxylating thioesterase. See, FIG. 9.

The percent identity (homology) between two amino acid sequences can be determined as follows. First, the amino acid sequences are aligned using the BLAST 2 Sequences (B12seq) program from the stand-alone version of BLASTZ containing BLASTP version 2.0.14. This stand-alone version of BLASTZ can be obtained from Fish & Richardson's web site (e.g., www.fr.com/blast/) or the U.S. government's National Center for Biotechnology Information web site (www.ncbi.nlm.nih.gov). Instructions explaining how to use the B12seq program can be found in the readme file accompanying BLASTZ. B12seq performs a comparison between two amino acid sequences using the BLASTP algorithm. To compare two amino acid sequences, the options of B12seq are set as follows: —i is set to a file containing the first amino acid sequence to be compared (e.g., C:\seq1.txt); —j is set to a file containing the second amino acid sequence to be compared (e.g., C:\seq2.txt); —p is set to blastp; —o is set to any desired file name (e.g., C:\output.txt); and all other options are left at their default setting. For example, the following command can be used to generate an output file containing a comparison between two amino acid sequences: C:\B12seq —i c:\seq1.txt —j c:\seq2.txt —p blastp —o c:\output.txt. If the two compared sequences share homology (identity), then the designated output file will present those regions of homology as aligned sequences. If the two compared sequences do not share homology (identity), then the designated output file will not present aligned sequences. Similar procedures can be following for nucleic acid sequences except that blastn is used.

Once aligned, the number of matches is determined by counting the number of positions where an identical amino acid residue is presented in both sequences. The percent identity (homology) is determined by dividing the number of matches by the length of the full-length polypeptide amino acid sequence followed by multiplying the resulting value by 100. It is noted that the percent identity (homology) value is rounded to the nearest tenth. For example, 78.11, 78.12, 78.13, and 78.14 is rounded down to 78.1, while 78.15, 78.16, 78.17, 78.18, and 78.19 is rounded up to 78.2. It also is noted that the length value will always be an integer.

It will be appreciated that a number of nucleic acids can encode a polypeptide having a particular amino acid sequence. The degeneracy of the genetic code is well known to the art; i.e., for many amino acids, there is more than one nucleotide triplet that serves as the codon for the amino acid. For example, codons in the coding sequence for a given enzyme can be modified such that optimal expression in a particular species (e.g., bacteria or fungus) is obtained, using appropriate codon bias tables for that species.

Functional fragments of any of the enzymes described herein can also be used in the methods of the document. The term “functional fragment” as used herein refers to a peptide fragment of a protein that has at least 25% (e.g., at least: 30%; 40%; 50%; 60%; 70%; 75%; 80%; 85%; 90%; 95%; 98%; 99%; 100%; or even greater than 100%) of the activity of the corresponding mature, full-length, wild-type protein. The functional fragment can generally, but not always, be comprised of a continuous region of the protein, wherein the region has functional activity.

This document also provides (i) functional variants of the enzymes used in the methods of the document and (ii) functional variants of the functional fragments described above. Functional variants of the enzymes and functional fragments can contain additions, deletions, or substitutions relative to the corresponding wild-type sequences. Enzymes with substitutions will generally have not more than 50 (e.g., not more than one, two, three, four, five, six, seven, eight, nine, ten, 12, 15,20,25,30,35,40, or 50) amino acid substitutions (e.g., conservative substitutions). This applies to any of the enzymes described herein and functional fragments. A conservative substitution is a substitution of one amino acid for another with similar characteristics. Conservative substitutions include substitutions within the following groups: valine, alanine and glycine; leucine, valine, and isoleucine; aspartic acid and glutamic acid; asparagine and glutamine; serine, cysteine, and threonine; lysine and arginine; and phenylalanine and tyrosine. The nonpolar hydrophobic amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan and methionine. The polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids include arginine, lysine and histidine. The negatively charged (acidic) amino acids include aspartic acid and glutamic acid. Any substitution of one member of the above-mentioned polar, basic or acidic groups by another member of the same group can be deemed a conservative substitution. By contrast, a nonconservative substitution is a substitution of one amino acid for another with dissimilar characteristics.

Deletion variants can lack one, two, three, four, five, six, seven, eight, nine, ten, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 amino acid segments (of two or more amino acids) or non-contiguous single amino acids. Additions (addition variants) include fusion proteins containing: (a) any of the enzymes described herein or a fragment thereof; and (b) internal or terminal (C or N) irrelevant or heterologous amino acid sequences. In the context of such fusion proteins, the term “heterologous amino acid sequences” refers to an amino acid sequence other than (a). A heterologous sequence can be, for example a sequence used for purification of the recombinant protein (e.g., FLAG, polyhistidine (e.g., hexahistidine), hemagluttanin (HA), glutathione-S-transferase (GST), or maltosebinding protein (MBP)). Heterologous sequences also can be proteins useful as detectable markers, for example, luciferase, green fluorescent protein (GFP), or chloramphenicol acetyl transferase (CAT). In some embodiments, the fusion protein contains a signal sequence from another protein. In certain host cells (e.g., yeast host cells), expression and/or secretion of the target protein can be increased through use of a heterologous signal sequence. In some embodiments, the fusion protein can contain a carrier (e.g., KLH) useful, e.g., in eliciting an immune response for antibody generation) or ER or Golgi apparatus retention signals. Heterologous sequences can be of varying length and in some cases can be a longer sequences than the full-length target proteins to which the heterologous sequences are attached.

Recombinant hosts can naturally express none or some (e.g., one or more, two or more, three or more, four or more, five or more, or six or more) of the enzymes of the pathways described herein. Endogenous genes of the recombinant hosts also can be disrupted to prevent the formation of undesirable metabolites or prevent the loss of intermediates in the pathway through other enzymes acting on such intermediates. Recombinant hosts can be referred to as recombinant host cells, engineered cells, or engineered hosts. Thus, as described herein, recombinant hosts can include nucleic acids encoding one or more of a decarboxylase, a kinase, a dehydrogenase, a monooxygenase, an acyl [acyl carrier protein (acp)] dehydrogenase, a dehydratase, a thioesterase, or a decarboxyating thioesterase as described in more detail below.

In addition, the production of isoprene can be performed in vitro using the isolated enzymes described herein, using a lysate (e.g., a cell lysate) from a host microorganism as a source of the enzymes, or using a plurality of lysates from different host microorganisms as the source of the enzymes.

Production of Branched C5 Central Metabolite Backbones

In some embodiments, 3-methyl-pent-2-enoyl-CoA or 4-methyl-pent-2-enoyl-CoA is formed by a 2-hydroxyacyl-CoA dehydratase classified, for example, under EC 4.2.1.-, such as the gene product of HadBC (SEQ ID NO: 3 and SEQ ID NO:4) and its initiator HadI (SEQ ID NO: 2), or by the gene product of HgdAB (SEQ ID NO: 6 and SEQ ID NO:7) and its initiator HdgC (SEQ ID NO: 5). See, FIG. 2-5.

In some embodiments, the 2-hydroxyacyl-CoA dehydratase is the result of enzyme engineering. The 2-hydroxyacyl-CoA dehydratase enzymes isolated from anaerobic bacteria possess a common catalytic mechanism employed in amino acid degradation pathways. For example, the gene products of HadBC/HadI from Clostridium difficile catalyse the conversion of (R)-2-hydroxyisocaproyl-CoA to isocaprenoyl-CoA. Similarly, the gene products of HgdAB/HdgC catalyse the conversion of 2-hydroxyglutaryl-CoA to glutaconyl-CoA (Kim et al., FEMS Microbiol. Reviews, 2004, 28, 455-468). See FIGS. 2-5.

In some embodiments, a 3-hydroxy functional group is introduced into 3-methyl-pent-2-enoyl-CoA or 4-methyl-pent-2-enoyl-CoA by a (R)-specific enoyl-CoA hydratase enzyme classified, for example, under EC 4.2.1.119 such as the gene product of phaJ (SEQ ID NO: 16, Fukui et al., J. Bacteriol., 1998, 180(3), 667-673) or MaoC (SEQ ID NO: 17; Park and Lee, J. Bacteriol., 2003, 185(18), 5291-5397) or a bacterial (S)-specific enoyl-CoA hydratase classified, for example, under EC 4.2.1.17 such as the gene product of YsiB (SEQ ID NO: 1). See, for example, FIGS. 4 and 5.

In some embodiments, the enoyl-CoA hydratase enzyme is the result of enzyme engineering. A single enzyme candidate for the introduction of a 3-hydroxy functional group into 3-methylbuten-2-enoyl-CoA has been identified previously in the cell free extract of Galactomyces reessii, containing an enoyl-CoA hydratase, classified in EC 4.2.1.17, that converts 3-methylbuten-2-enoyl-CoA to 3-hydroxy-3-methylbutanoyl-CoA (Lee et al., Appl. Environ. Microbiol., 1997, 63(11), 4191-4195). Equivalent enoyl-CoA hydratase activity from bacterial origin has not been identified. See FIG. 4 and FIG. 5.

In some embodiments, 4-methyl-3-oxopentanoyl-ACP is formed by condensing isobutyryl-CoA and malonyl-ACP using a β-ketoacyl-ACP-synthase enzyme classified, for example, under EC 2.3.1.- (e.g., EC 2.3.1.41, EC 2.3.1.79, or EC 2.3.1.80) such as the gene product of AnlF (SEQ ID NO: 18). It has been demonstrated that the gene product of anlF condenses isobutyryl-CoA and malonyl-ACP (Lechner et al., ACS Synth. Biol., 2013, 2(7), 379-83). See, FIG. 6.

In some embodiments (FIG. 8), the central precursor to 3-methyl-3-hydroxypent-4-enoate, acetyl-CoA, is converted to acetoacetyl-CoA by an acetyl-CoA C-acetyltransferase classified, for example, under EC 2.3.1.9, followed by conversion to 3-hydroxy-3-methylglutaryl-CoA by a hydroxymethylglutaryl-CoA synthase classified, for example, under EC 2.3.3.10; followed by conversion to (R)-mevalonate by a hydroxymethylglutaryl-CoA reductase classified under EC 1.1.1.88 or EC 1.1.1.34; followed by conversion to 3-methyl-3-hydroxypent-4-enoate by an enzyme classified, for example, under EC 4.2.1.- such as an oleate hydratase, (e.g., a the gene product of ohyA (SEQ ID NO: 22) or a dehydratase classified under EC 4.2.1.- (such as one isolated from species such as Aquincola tertiaricarbonis or Methylibium petroleiphilum PM1).

In some embodiments, the dehydratase enzyme converting mevalonate to 3-methyl-3-hydroxypent-4-enoate is the result of enzyme engineering to improve activity or specificity using the structure and wild-type residue diversity of, for example, an oleate hydratase (SEQ ID NO: 22).

Enzymes Generating First Terminal Vinyl Group

In some embodiments, a first terminal vinyl group is introduced into 3-methyl-pent-2-enoyl-ACP, forming 3-methyl-pent-2,4-dienoyl-[acp] and then enzymatically converted in one or more steps to 3-methyl-3-hydroxypent-4-enoate or 3-methyl-3-sulphoryl-pent-4-enoyl-ACP (as shown, for example, in FIG. 2). It has been demonstrated that the gene product of tcsD (SEQ ID NO: 14) from Streptomyces kanamyceticus has dehydrogenase activity for straight and branch chain C5 acyl-ACP substrates (Mo et al., JACS, 2011, 133, 976-985). 3-methyl-pent-2-enoyl-ACP can be derived from the central metabolite 3-methyl-2-oxopentanoate.

In some embodiments, a first terminal vinyl group is introduced into 4-methyl-pent-2-enoyl-[acp], forming 4-methyl-pent-2,4-dienoyl-[acp], which may be enzymatically converted in one or more steps to 4-methyl-3-hydroxypent-4-enoate (see, for example FIG. 3 and FIG. 6), 4-methyl-3-sulphoryl-pent-4-enoyl-ACP (see, for example, FIG. 3 and FIG. 6), or 3-methyl-3-buten-2-ol (see, for example, FIG. 3 and FIG. 7). It has been demonstrated that the gene product of tcsD (SEQ ID NO: 14) from Streptomyces kanamyceticus has dehydrogenase activity for 4-methyl-pent-2-enoyl-ACP (Mo et al., 2011, supra). 4-methyl-pent-2-enoyl-[acp] can be derived from the central metabolite 4-methyl-2-oxopentanoate or isobutyryl-CoA.

In some embodiments, the first vinyl group is introduced into 3-methyl-3-hydroxy-pentanoate by a monooxgyenase, forming 3-methyl-3-hydroxy-pent-4-enoate (see, for example, FIG. 4). It has been demonstrated that the monooxygenase encoded by mdpJ (SEQ ID NO: 15) introduces a terminal double bond into allyl groups bound to a secondary alcohol (Schäfer et al., Appl. Environ. Microbiol., 2012, 78(17), 6280-6284).

In some embodiments, the first vinyl group is introduced into 4-methyl-3-hydroxypentanoate, forming 4-methyl-3-hydroxypent-4-enoate (see, for example, FIG. 5).

In some embodiments, the first vinyl group is introduced into mevalonate, forming 3-hydroxy-3-methyl-pent-4-enoate (as shown, for example, in FIG. 8).

Enzymes Generating Second Terminal Vinyl Group and Producing Isoprene

In some embodiments, the second vinyl group is introduced into a medium chain carbon alkenoate such as 3-methyl-3-hydroxypent-4-enoate or 4-methyl-3-hydroxypent-4-enoate by a GHMP superfamily enzyme such as a mevalonate diphosphate decarboxylase classified, for example, under EC 4.1.1.33 (e.g., SEQ ID NOs: 8-11) (Lefurgy et al., J. Biol. Chem., 2010, 285(27), 20654-20663)) or a mevalonate 3-kinase classified, for example, under EC 2.7.1.- (e.g., SEQ ID NO: 12) (Vinokur et al., Biochemistry, 2014, 53(25), 4161-4168), producing isoprene (FIGS. 2-6 and 8). In some embodiments, a MDD has an amino acid substitution at one or both positions corresponding to amino acids 74 and/or 145 of the amino acid sequence set forth in SEQ ID NO:11. For example, a histidine residue can be substituted for arginine at a position aligning with residue 74 of SEQ ID NO:11 and/or a phenylalanine residue can be substituted for an isoleucine at a position aligning with residue 145 of SEQ ID NO:11. In some embodiments, a MDD has the amino acid sequence set forth in SEQ ID NO:11, except that a histidine is substituted at position 74 for arginine and/or a phenylalanine is substituted at position 145 for isoleucine.

In some embodiments, the second vinyl group is introduced into medium chain carbon alkenoate such as 3-methyl-3-sulphoryl-pent-4-enoyl-ACP or 4-methyl-3-sulphoryl-pent-4-enoyl-ACP by a decarboxylating thioesterase (e.g., from Lyngbya majuscula (CurM TE), Moorea producens (SEQ ID NO: 21), Pseudomonas entomophila, H. ochraceum, Synechococcus PCC 7002, Cyanothece PCC 7424 or Cyanothece PCC 7822) (see Gehret et al., J. Biol. Chem., 2011, 286(16), 14445-14454), converting 3-methyl-3-sulphoryl-pent-4-enoyl-ACP or 4-methyl-3-sulphoryl-pent-4-enoyl-ACP to isoprene (see, FIG. 2, FIG. 3 and FIG. 6).

In some embodiments, the second vinyl group is introduced into a medium chain carbon alkenoate such as 3-methyl-3-buten-2-ol by a linalool dehydratase classified, for example, under EC 4.2.1.- such as EC 4.2.1.127 (SEQ ID NO: 13, GenBank Accession No. CBW30776.1, Brodkorb et al., J. Biol. Chem., 2010, 285(40), 30436-30442) or a dehydratase classified under EC 4.2.1.- such as one isolated from a species such as Aquincola tertiaricarbonis or Methylibium petroleiphilum PM1; Schäfer et al., Appl. Environ. Microbiol., 2011, 77(17), 5981-5987). See, FIG. 3 and FIG. 7.

Pathways to 3-Methyl-3-Hydroxypent-4-Enoyl-[acp]

In some embodiments (FIG. 2), the central precursor to 3-methyl-3-hydroxypent-4-enoyl-[acp], 3-methyl-2-oxo-pentanoate, is converted to 3-methyl-2-hydroxypentanoate by a (R)-2-hydroxyacyl dehydrogenase classified, for example, under EC 1.1.1.272 such as the gene product of ldhA, followed by conversion to 3-methyl-2-hydroxy-pentanoyl-CoA by a CoA-transferase such as the gene product of HadA or GctAB (e.g., a glutaconate CoA transferase classified, for example, under EC 2.8.3.12) or a CoA-ligase classified, for example, under EC 6.2.1.- (e.g., EC 6.2.1.2); followed by conversion to 3-methyl-pent-2-enoyl-CoA by a (R)-2-Hydroxyacyl-CoA dehydratase such as the gene products of HadBC (SEQ ID NOs: 3 and 4) and the initiator HadI (SEQ ID NO: 2) or the gene products of HgdAB (SEQ ID NOs: 6 and 7) and the initiator HgdC (SEQ ID NO: 5); followed by conversion to 3-methyl-pent-2-enoyl-[acp] by an acyl transferase such as encoded by tcsA (see Genbank Accession No. ADU56236.1) or a 4′ phosphopantetheinyl transferase such as encoded by sfp (see Genbank Accession No. CAA44858.1) or svp (see Genbank Accession No. AAG43513.1); followed by conversion to 3-methyl-pent-2,4-dienoyl-ACP by an acyl-[acp] dehydrogenase such as the gene product of TcsD (SEQ ID NO:14); followed by conversion to 3-methyl-3-hydroxypent-4-enoyl-ACP by a 3-hydroxyacyl-[acp] dehydratase classified, for example, under EC 4.2.1.59.

In some embodiments (FIG. 2), 3-methyl-3-hydroxypent-4-enoyl-[acp], a central precursor to 3-methyl-3-hydroxypent-4-enoate, is converted to 3-methyl-3-hydroxypent-4-enoyl-CoA by a (R)-3-hydroxyacyl-ACP:CoA transacylase such as the gene product of PhaG; followed by conversion to 3-methyl-3-hydroxypent-4-enoate by a CoA-tranferase such as the gene product of HadA or GctAB or by a thioesterase classified, for example, under EC 3.1.2.—such as the gene product of tesB (e.g., GenBank Accession No. AAA24665.1) or YciA (See Genbank Accession No. BAA14785.1).

In some embodiments (FIG. 2), 3-methyl-3-hydroxypent-4-enoyl-ACP, a central precursor to 3-methyl-3-hydroxypent-4-enoate, is converted to 3-methyl-3-hydroxypent-4-enoate by a thioesterase such as an acyl [acp] thioesterase (e.g., the gene product encoded by GenBank Accession No. AA077182 or CCC78182.1).

In some embodiments (FIG. 2), 3-methyl-3-hydroxypent-4-enoyl-[acp], the central precursor to 3-methyl-3-sulphoryl-pent-4-enoyl-[acp], is converted to 3-methyl-3-sulphoryl-pent-4-enoyl-[acp] by a sulfotransferase classified under EC 2.8.2.—such as the gene product of CurM ST or OLS ST.

Pathways to 4-Methyl-3-Hydroxypent-4-Enoyl-[acp]

In some embodiments (FIG. 3), the central precursor to 4-methyl-3-hydroxypent-4-enoyl-[acp], 4-methyl-2-oxo-pentanoate, is converted to 4-methyl-2-hydroxypentanoate by a (R)-2-hydroxyacyl dehydrogenase classified, for example, under EC 1.1.1.272 such as the gene product of ldhA, followed by conversion to 4-methyl-2-hydroxy-pentanoyl-CoA by a CoA-transferase such as the gene product of HadA or GctAB or a CoA-ligase such as classified under EC 6.2.1.-(2); followed by conversion to 4-methyl-pent-2-enoyl-CoA by a (R)-2-Hydroxyacyl-CoA dehydratase such as the gene products HadBC and the initiator HadI; followed by conversion to 4-methyl-pent-2-enoyl-[acp] by an acyl transferase such as the reaction with the gene product from TcsA & sfp/svp; followed by conversion to 4-methyl-pent-2,4-dienoyl-[acp] by an acyl-ACP dehydrogenase such as the gene product of TcsD; followed by conversion to 4-methyl-3-hydroxypent-4-enoyl-[acp] by a 3-hydroxyacyl-[acp] dehydratase classified, for example, under EC 4.2.1.59 such as the gene product of fabZ.

In some embodiments (FIG. 6), the central precursor to 4-methyl-3-hydroxypent-4-enoyl-[acp], isobutyryl-CoA, is converted to 4-methyl-3-oxo-pentanoyl-[acp] by a β-ketoacyl-[acp]-synthase such as the gene product of AnIF; followed by conversion to 4-methyl-3-hydroxy-pentanoyl-[acp] by a 3-oxoacyl-[acp] reductase (EC 1.1.1.100) such as the gene product of fabG or AnlG; followed by conversion to 4-methyl-pent-2-enoyl-[acp] by a 3-hydroxyacyl-[acp] dehydratase (EC 4.2.1.59) such as the gene product of fabZ; followed by conversion to 4-methyl-pent-2,4-dienoyl-[acp] by an acyl-[acp] dehydrogenase such as the gene product of tcsD; followed by conversion to 4-methyl-3-hydroxypent-4-enoyl-[acp] by a 3-hydroxyacyl-[acp] hydratase such as EC 4.2.1.59 such as the gene product of fabZ.

In some embodiments (FIG. 7), the central precursor to 4-methyl-3-hydroxypent-4-enoyl-[acp], isobutyryl-CoA, is converted to 4-methyl-3-oxo-pentanoyl-[acp] by a β-ketoacyl-[acp]-synthase such as the gene product of AnlF; followed by conversion to 4-methyl-3-hydroxy-pentanoyl-[acp] by a 3-oxoacyl-[acp] reductase (EC 1.1.1.100) such as the gene product of fabG or AnlG; followed by conversion to 4-methyl-pent-2-enoyl-[acp] by a 3-hydroxyacyl-[acp] dehydratase (EC 4.2.1.59) such as the gene product of fabZ; followed by conversion to 4-methyl-pent-2,4-dienoyl-[acp] by an acyl-[acp] dehydrogenase such as the gene product of tcsD; followed by conversion to 4-methyl-3-hydroxypent-4-enoyl-[acp] by a 3-hydroxyacyl-ACP hydratase such as EC 4.2.1.59 such as the gene product of fabZ.

Pathways to 3-Methyl-3-Hydroxypent-4-Enoate

In some embodiments (FIG. 2), the central precursor to 3-methyl-3-hydroxypent-4-enoate, 3-methyl-3-hydroxypent-4-enoyl-[acp], is converted to 3-methyl-3-hydroxypent-4-enoyl-CoA by a (R)-3-hydroxyacyl-[acp]: CoA transacylase such as the gene product of PhaG; followed by conversion to 3-methyl-3-hydroxypent-4-enoate by a CoA-transferase such as the gene product of HadA or GctAB or by a thioesterase such as the gene product of tesB (e.g., GenBank Accession No. AAA24665.1) or YciA (See Genbank Accession No. BAA14785.1).

In some embodiments (FIG. 2), the central precursor to 3-methyl-3-hydroxypent-4-enoate, 3-methyl-3-hydroxypent-4-enoyl-[acp], is converted to 3-methyl-3-hydroxypent-4-enoate by a thioesterase classified, for example, under EC 3.2.1.- such as the Bacteroides thetaiotaomicron acyl-[acp] thioesterase (GenBank Accession No. AA077182) or Lactobacillus plantarum thioesterase (GenBank Accession No. CCC78182.1).

In some embodiments (FIG. 4), the central precursor to 3-methyl-3-hydroxypent-4-enoate, 3-methyl-2-oxo-pentanoate, is converted to 3-methyl-2-hydroxypentanoate by a (R)-2-hydroxyacyl dehydrogenase classified, for example, under EC 1.1.1.272 such as the gene product of ldhA, followed by conversion to 3-methyl-2-hydroxy-pentanoyl-CoA by a CoA-transferase such as the gene product of HadA or GctAB or a CoA-ligase such as classified under EC 6.2.1.- (e.g., EC 6.2.1.2); followed by conversion to 3-methyl-pent-2-enoyl-CoA by a (R)-2-Hydroxyacyl-CoA dehydratase such as the gene products of HadBC (SEQ ID NOs: 3 and 4) and the initiator HadI (SEQ ID NO:2) or the gene product HgdAB (SEQ ID NOs: 6 and 7) and the initiator HgdC (SEQ ID NO:5); followed by conversion to 3-methyl-3-hydroxypentanoyl-CoA by an enoyl-CoA hydratase such as the gene product of phaJ (SEQ ID NO:16), MaoC (SEQ ID NO: 17) or YsiB (SEQ ID NO: 1); followed by conversion to 3-methyl-3-hydroxypentanoate by a CoA-transferase such as the gene product of HadA or GctAB or a thioesterase such as the gene product of tesB (e.g., GenBank Accession No. AAA24665.1) or YciA (see Genbank Accession No. BAA14785.1); followed by conversion to 3-methyl-3-hydroxypent-4-enoate by a monooxygenase such as the gene product of MdpJ (SEQ ID NO: 15) or a cytochrome P450 such as the gene product of the CYP4 family.

In some embodiments, the enzymes shown in FIG. 4 are the result of enzyme engineering to improve activity or specificity using the enzyme structure and wild-type residue diversity to inform the rational enzyme design.

Pathways to 4-Methyl-3-Hydroxypent-4-Enoate

In some embodiments (FIG. 3 and FIG. 6), the central precursor to 4-methyl-3-hydroxypent-4-enoate, 4-methyl-3-hydroxypent-4-enoyl-[acp], is converted to 4-methyl-3-hydroxypent-4-enoyl-CoA by (R)-3-hydroxyacl-[acp]: CoA transacylase such as the gene product of PhaG; followed by conversion to 4-methyl-3-hydroxypent-4-enoate by a CoA-tranferase such as the gene product of HadA or GctAB or by a thioesterase such as the gene product of tesB (e.g., GenBank Accession No. AAA24665.1) or YciA (see Genbank Accession No. BAA14785.1).

In some embodiments (FIG. 3 and FIG. 6), the central precursor to 4-methyl-3-hydroxypent-4-enoate, 4-methyl-3-hydroxypent-4-enoyl-[acp], is converted to 4-methyl-3-hydroxypent-4-enoate by a thioesterase classified, for example, under EC 3.2.1.- such as the Bacteroides thetaiotaomicron acyl-[acp] thioesterase (GenBank Accession No. AA077182) or Lactobacillus plantarum thioesterase (GenBank Accession No. CCC78182.1).

In some embodiments (FIG. 5), the central precursor to 4-methyl-3-hydroxypent-4-enoate, 4-methyl-2-oxo-pentanoate, is converted to 4-methyl-2-hydroxypentanoate by a (R)-2-hydroxyacyl dehydrogenase classified, for example, under EC 1.1.1.272 such as the gene product of ldhA, followed by conversion to 4-methyl-2-hydroxy-pentanoyl-CoA by a CoA-transferase such as the gene product of HadA or GctAB or a CoA-ligase classified, for example, under EC 6.2.1.- (e.g., EC 6.2.1.2); followed by conversion to 4-methyl-pent-2-enoyl-CoA by a (R)-2-Hydroxyacyl-CoA dehydratase such as the gene products of HadBC (SEQ ID NOs: 3 and 4) and the initiator HadI (SEQ ID NO: 2) or the gene products of HgdAB (SEQ ID NO: 6 and 7) and the initiator HgdC (SEQ ID NO:5); followed by conversion to 4-methyl-3-hydroxypentanoyl-CoA by an enoyl-CoA hydratase such as the gene product of phaJ (SEQ ID NO: 16), MaoC (SEQ ID NO: 17) or YsiB (SEQ ID NO: 1); followed by conversion to 4-methyl-3-hydroxypentanoate by a CoA-transferase such as the gene product of HadA or GctAB or a thioesterase such as the gene product of tesB (e.g., GenBank Accession No. AAA24665.1) or YciA (e.g., Genbank Accession No. BAA14785.1); followed by conversion to 4-methyl-3-hydroxypent-4-enoate by a monooxygenase such as the gene product of MdpJ (SEQ ID NO: 15) or a cytochrome P450 such as the gene product of the CYP4 family.

In some embodiments, the enzymes shown in FIG. 5 are the result of enzyme engineering to improve activity or specificity using the enzyme structure and wild-type residue diversity to inform the rational enzyme design.

Pathway to 4-Methyl-3-Sulphoryl-Pent-4-Enoyl-[acp]

In some embodiments, the central precursor to 4-methyl-3-sulphoryl-pent-4-enoyl-[acp], 4-methyl-3-hydroxypent-4-enoyl-[acp], is converted to 4-methyl-3-sulphoryl-pent-4-enoyl-[acp] by a sulfotransferase such as the gene product of CurM ST or OLS ST. See, FIG. 3 and FIG. 6.

Pathways to 3-Methyl-3-Buten-2-ol

In some embodiments (e.g., FIG. 3 and FIG. 7), the central precursor to 3-methyl-3-buten-2-ol, 4-methyl-3-hydroxypent-4-enoyl-[acp], can be converted to 4-methyl-3-hydroxypent-4-enoyl-[acp] by (R)-3-hydroxyacyl-[acp]: CoA transacylase such as the gene product of PhaG; followed by conversion to 4-methyl-3-oxopent-4-enoyl-CoA by a dehydrogenase classified, for example under EC 1.1.1.- such as EC 1.1.1.36 or EC 1.1.1.157); followed by conversion to 4-methyl-3-oxopent-4-enoate by a thioesterase classified for example, under EC 3.2.1.11 or a CoA-transferase classified under EC 2.8.3.—encoded by AtoAD or pcaIJ; followed by conversion to 3-methyl-3-buten-2-one by an acetoacetate decarboxylase classified, for example, under EC 4.1.1.4; followed by conversion to 3-methyl-3-buten-2-ol by a secondary alcohol dehydrogenase, classified, for example, under EC 1.1.1.B3, EC 1.1.1.B4 or EC 1.1.1.80.

In some embodiments (e.g., FIG. 3 and FIG. 7), the central precursor to 3-methyl-3-buten-2-ol, 4-methyl-3-hydroxypent-4-enoyl-[acp], can be converted to 4-methyl-3-oxopent-4-enoyl-[acp] by a 3-oxoacyl-[acp] reductase such as an enzyme classified under EC 1.1.1.100 (e.g., the gene product of fabG or AnlG); following by conversion to 4-methyl-3-oxopent-4-enoate by a thioesterase classified, for example, under EC 3.1.2.—such as the Bacteroides thetaiotaomicron acyl-[acp] thioesterase (GenBank Accession No. AA077182) or Lactobacillus plantarum thioesterase (GenBank Accession No. CCC78182.1); followed by conversion to 3-methyl-3-buten-one by an acetoacetate decarboxylase classified, for example, under EC 4.1.1.4; followed by conversion to 3-methyl-3-buten-2-ol by a secondary alcohol dehydrogenase, classified, for example, under EC 1.1.1.B3, EC 1.1.1.B4 or EC 1.1.1.80.

In some embodiments, the enzymes shown in FIG. 3 and FIG. 7 are the result of enzyme engineering to improve activity or specificity using the enzyme structure and wild-type residue diversity to inform the rational enzyme design.

In some embodiments, the enzymes shown in FIG. 3 and FIG. 7 are the result of enzyme engineering to improve activity or specificity using the enzyme structure and wild-type residue diversity to inform the rational enzyme design.

Cultivation Strategies

In some embodiments, the nucleic acids encoding the enzymes of the pathways described in FIGS. 2-8 are introduced into a host microorganism that is either a prokaryote or eukaryote.

For example, the prokaryote can be a bacterium from the genus Escherichia such as Escherichia coli; from the genus Clostridia such as Clostridium ljungdahlii, Clostridium autoethanogenum or Clostridium kluyveri; from the genus Corynebacteria such as Corynebacterium glutamicum; from the genus Cupriavidus such as Cupriavidus necator or Cupriavidus metallidurans; from the genus Pseudomonas such as Pseudomonas fluorescens, Pseudomonas putida or Pseudomonas oleavorans; from the genus Delftia such as Delftia acidovorans; from the genus Bacillus such as Bacillus subtillis; from the genus Lactobacillus such as Lactobacillus delbrueckii; or from the genus Lactococcus such as Lactococcus lactis. Such prokaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of producing isoprene or precursors thereof.

In some embodiments, the host microorganism is a eukaryote. For example, the eukaryote can be a filamentous fungus, e.g., one from the genus Aspergillus such as Aspergillus niger. Alternatively, the eukaryote can be a yeast, e.g., one from the genus Saccharomyces such as Saccharomyces cerevisiae; from the genus Pichia such as Pichia pastoris; or from the genus Yarrowia such as Yarrowia lipolytica; from the genus Issatchenkia such as Issathenkia orientalis; from the genus Debaryomyces such as Debaryomyces hansenii; from the genus Arxula such as Arxula adenoinivorans; or from the genus Kluyveromyces such as Kluyveromyces lactis. Such eukaryotes also can be a source of genes to construct recombinant host cells described herein that are capable of producing isoprene or precursors thereof.

In some embodiments, isoprene is biosynthesized in a recombinant host using a fermentation strategy that can include anaerobic, micro-aerobic or aerobic cultivation of the recombinant host.

In some embodiments, isoprene is biosynthesized in a recombinant host using a fermentation strategy that uses an alternate final electron acceptor to oxygen such as nitrate.

In some embodiments, a cell retention strategy using, for example, ceramic hollow fiber membranes can be employed to achieve and maintain a high cell density during either fed batch or continuous fermentation in the synthesis of isoprene.

In some embodiments, the biological feedstock can be, can include, or can derive from, monosaccharides, disaccharides, lignocellulose, hemicellulose, cellulose, lignin, levulinic acid & formic acid, triglycerides, glycerol, fatty acids, agricultural waste, condensed distillers' solubles or municipal waste.

The efficient catabolism of crude glycerol stemming from the production of biodiesel has been demonstrated in several microorganisms such as Escherichia coli, Cupriavidus necator, Pseudomonas oleavorans, Pseudomonas putida and Yarrowia lipolytica (Lee et al., Appl. Biochem. Biotechnol., 2012, 166, 1801-1813; Yang et al., Biotechnology for Biofuels, 2012, 5:13; Meijnen et al., Appl. Microbiol. Biotechnol., 2011, 90, 885-893).

The efficient catabolism of lignocellulosic-derived levulinic acid has been demonstrated in several organisms such as Cupriavidus necator and Pseudomonas putida in the synthesis of 3-hydroxyvalerate via the precursor propanoyl-CoA (Jaremko and Yu, Journal of Biotechnology, 2011, 155, 2011, 293-298; Martin and Prather, Journal of Biotechnology, 2009, 139, 61-67).

The efficient catabolism of lignin-derived aromatic compounds such benzoate analogues has been demonstrated in several microorganisms such as Pseudomonas putida, Cupriavidus necator (Bugg et al., Current Opinion in Biotechnology, 2011, 22, 394-400; Perez-Pantoja et al., FEMS Microbiol. Rev., 2008, 32, 736-794).

The efficient utilization of agricultural waste, such as olive mill waste water has been demonstrated in several microorganisms, including Yarrowia lipolytica (Papanikolaou et al., Bioresour. Technol., 2008, 99(7), 2419-2428).

The efficient utilization of fermentable sugars such as monosaccharides and disaccharides derived from cellulosic, hemicellulosic, cane and beet molasses, cassava, corn and other argricultural sources has been demonstrated for several microorganism such as Escherichia coli, Corynebacterium glutamicum and Lactobacillus delbrueckii and Lactococcus lactis (see, e.g., Hermann et al, Journal of Biotechnology, 2003, 104, 155-172; Wee et al., Food Technol. Biotechnol., 2006, 44(2), 163-172; Ohashi et al., Journal of Bioscience and Bioengineering, 1999, 87(5), 647-654).

The efficient utilization of furfural, derived from a variety of agricultural lignocellulosic sources, has been demonstrated for Cupriavidus necator (Li et al., Biodegradation, 2011, 22, 1215-1225).

In some embodiments, the non-biological feedstock can be or can derive from natural gas, syngas, CO₂/H₂, methanol, ethanol, benzoic acid, non-volatile residue (NVR) or a caustic wash waste stream from cyclohexane oxidation processes, or terephthalic acid/isophthalic acid mixture waste streams.

The efficient catabolism of methanol has been demonstrated for the methylotropic yeast Pichia pastoris.

The efficient catabolism of ethanol has been demonstrated for Clostridium kluyveri (Seedorf et al., Proc. Natl. Acad. Sci. USA, 2008, 105(6) 2128-2133).

The efficient catabolism of CO₂ and H₂, which may be derived from natural gas and other chemical and petrochemical sources, has been demonstrated for Cupriavidus necator (Prybylski et al., Energy, Sustainability and Society, 2012, 2:11).

The efficient catabolism of syngas has been demonstrated for numerous microorganisms, such as Clostridium ljungdahlii and Clostridium autoethanogenum (Köpke et al., Applied and Environmental Microbiology, 2011, 77(15), 5467-5475).

The efficient catabolism of the non-volatile residue waste stream from cyclohexane processes has been demonstrated for numerous microorganisms, such as Delftia acidovorans and Cupriavidus necator (Ramsay et al., Applied and Environmental Microbiology, 1986, 52(1), 152-156).

In some embodiments, substantially pure cultures of recombinant host microorganisms are provided. As used herein, a “substantially pure culture” of a recombinant host microorganism is a culture of that microorganism in which less than about 40% (i.e., less than about 35%; 30%; 25%; 20%; 15%; 10%; 5%; 2%; 1%; 0.5%; 0.25%; 0.1%; 0.01%; 0.001%; 0.0001%; or even less) of the total number of viable cells in the culture are viable cells other than the recombinant microorganism, e.g., bacterial, fungal (including yeast), mycoplasmal, or protozoan cells. The term “about” in this context means that the relevant percentage can be 15% of the specified percentage above or below the specified percentage. Thus, for example, about 20% can be 17% to 23%. Such a culture of recombinant microorganisms includes the cells and a growth, storage, or transport medium. Media can be liquid, semi-solid (e.g., gelatinous media), or frozen. The culture includes the cells growing in the liquid or in/on the semi-solid medium or being stored or transported in a storage or transport medium, including a frozen storage or transport medium. The cultures are in a culture vessel or storage vessel or substrate (e.g., a culture dish, flask, or tube or a storage vial or tube).

Metabolic Engineering

The present document provides methods involving less than all the steps described for all the above pathways. Such methods can involve, for example, one, two, three, four, five, six, seven, eight, nine, ten, or more of such steps. Where less than all the steps are included in such a method, the first step can be any one of the steps listed. Furthermore, recombinant hosts described herein can include any combination of the above enzymes such that one or more of the steps, e.g., one, two, three, four, five, six, seven, eight, nine, ten, or more of such steps, can be performed within a recombinant host.

In addition, this document recognizes that where enzymes have been described as accepting CoA-activated substrates, analogous enzyme activities associated with [acp]-bound substrates exist that are not necessarily in the same enzyme class.

Also, this document recognizes that where enzymes have been described accepting (R)-enantiomers of substrate, analogous enzyme activities associated with (S)-enantiomer substrates exist that are not necessarily in the same enzyme class.

This document also recognizes that where an enzyme is shown to accept a particular co-factor, such as NADPH, or co-substrate, such as acetyl-CoA, many enzymes are promiscuous in terms of accepting a number of different co-factors or co-substrates in catalyzing a particular enzyme activity. Also, this document recognizes that where enzymes have high specificity for e.g., a particular co-factor such as NADH, an enzyme with similar or identical activity that has high specificity for the co-factor NADPH may be in a different enzyme class.

In some embodiments, the enzymes in the pathways outlined herein can be the result of enzyme engineering via non-direct or rational enzyme design approaches with aims of improving activity, improving specificity, reducing feedback inhibition, reducing repression, improving enzyme solubility, changing stereo-specificity, or changing co-factor specificity.

In some embodiments, the enzymes in the pathways outlined herein can be gene dosed, i.e., overexpressed, into the resulting genetically modified organism via episomal or chromosomal integration approaches.

In some embodiments, genome-scale system biology techniques such as Flux Balance Analysis can be utilized to devise genome scale attenuation or knockout strategies for directing carbon flux to isoprene.

Attenuation strategies include, but are not limited to, the use of transposons, homologous recombination (double cross-over approach), mutagenesis, enzyme inhibitors and RNAi interference.

In some embodiments, fluxomic, metabolomic and transcriptomal data can be utilized to inform or support genome-scale system biology techniques, thereby devising genome scale attenuation or knockout strategies in directing carbon flux to isoprene.

In some embodiments using hosts that naturally accumulate polyhydroxyalkanoates, the polymer synthase enzymes can be attenuated in the host strain.

In some embodiments, the enzymes from the mevalonate pathway, for example, EC 2.3.1.9, EC 2.3.3.10, EC 1.1.1.34 or EC 1.1.1.88, are introduced or gene dosed into a host microorganism that utilizes the non-mevalonate or 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid synthesis.

In some embodiments, the enzymes from the non-mevalonate or 2-C-methyl-D-erythritol 4-phosphate pathway leading to isoprenoid synthesis are introduced into a host microorganism that utilizes the mevalonate pathway for isoprenoid synthesis and EC 2.7.1.36 is attenuated.

In some embodiments, the enzymes responsible for 3′-Phosphoadenosine-5′-phosphosulfate (PAPS) synthesis classified under EC 2.7.7.4 & EC 2.7.1.25 are constitutively expressed in the host organisms.

In some embodiments requiring the intracellular availability of pyruvate for isoprene synthesis, a gene in an acetate synthesis pathway encoding an acetate kinase, such as ack, can be attenuated (Shen et al., Appl. Environ. Microbiol., 2011, 77(9), 2905-2915).

In some embodiments requiring the intracellular availability of pyruvate for isoprene synthesis, a gene encoding the degradation of pyruvate to lactate such as ldhA can be attenuated (Shen et al., Appl. Environ. Microbiol., 2011, 77(9), 2905-2915).

In some embodiments requiring the intracellular availability of pyruvate for isoprene synthesis, a gene encoding the degradation of phosphoenolpyruvate to succinate such as frdBC can be attenuated (see, e.g., Shen et al., 2011, supra).

In some embodiments requiring the intracellular availability of pyruvate for isoprene synthesis, a gene encoding the degradation of acetyl-CoA to ethanol such as adhE can be attenuated (Shen et al., 2011, supra).

In some embodiments, where pathways require excess NADPH co-factor in the synthesis of isoprene, a puridine nucleotide transhydrogenase gene such as UdhA can be overexpressed in the host organism (Brigham et al., Advanced Biofuels and Bioproducts, 2012, Chapter 39, 1065-1090).

In some embodiments, where pathways require excess NADPH co-factor in the synthesis of isoprene, a glyceraldehyde-3P-dehydrogenase gene such as GapN can be overexpressed in the host organism (Brigham et al., 2012, supra).

In some embodiments, where pathways require excess NADPH co-factor in the synthesis of isoprene, a malic enzyme gene such as macA or maeB can be overexpressed in the host organism (Brigham et al., 2012, supra).

In some embodiments, where pathways require excess NADPH co-factor in the synthesis of isoprene, a glucose-6-phosphate dehydrogenase gene such as zwf can be overexpressed in the host organism (Lim et al., Journal of Bioscience and Bioengineering, 2002, 93(6), 543-549).

In some embodiments, where pathways require excess NADPH co-factor in the synthesis of isoprene, a fructose 1,6 diphosphatase gene such as fbp can be overexpressed in the host (Becker et al., Journal of Biotechnology, 2007, 132, 99-109).

In some embodiments, a feedback inhibition resistant mutant of an acetolactate synthase classified, for example, under EC 2.2.1.6, such as mutants of ilvB and/or ilvN that are resistant to feedback inhibition by lysine and leucine, can be overexpressed in the host.

In some embodiments, acetolactate synthase can be expressed under a promoter not subject to genetic repression by branch-chain amino acids (e.g., valine, leucine, or isoleucine).

In some embodiments, the efflux of isoprene across the cell membrane to the extracellular media can be enhanced or amplified by genetically engineering structural modifications to the cell membrane or increasing any associated transporter activity for isoprene.

Producing Isoprene Using a Recombinant Host

Typically, isoprene is produced by providing a host microorganism and culturing the provided microorganism with a culture medium containing a suitable carbon source as described above. In general, the culture media and/or culture conditions can be such that the microorganisms grow to an adequate density and produce isoprene efficiently. For large-scale production processes, any method can be used such as those described elsewhere (Manual of Industrial Microbiology and Biotechnology, 2^(nd) Edition, Editors: A. L. Demain and J. E. Davies, ASM Press; and Principles of Fermentation Technology, P. F. Stanbury and A. Whitaker, Pergamon). Briefly, a large tank (e.g., a 100 gallon, 200 gallon, 500 gallon, or more tank) containing an appropriate culture medium is inoculated with a particular microorganism. After inoculation, the microorganism is incubated to allow biomass to be produced. Once a desired biomass is reached, the broth containing the microorganisms can be transferred to a second tank. This second tank can be any size. For example, the second tank can be larger, smaller, or the same size as the first tank. Typically, the second tank is larger than the first such that additional culture medium can be added to the broth from the first tank. In addition, the culture medium within this second tank can be the same as, or different from, that used in the first tank.

Once transferred, the microorganisms can be incubated to allow for the production of isoprene. Once produced, any method can be used to isolate isoprene.

Once produced, any method can be used to isolate isoprene. For example, isoprene can be recovered from the fermenter off-gas stream as a volatile product as the boiling point of isoprene is 34.1° C. At a typical fermentation temperature of approximately 30° C., isoprene has a high vapour pressure and can be stripped by the gas flow rate through the broth for recovery from the off-gas. Isoprene can be selectively adsorbed onto, for example, an adsorbent and separated from the other off-gas components. Membrane separation technology may also be employed to separate isoprene from the other off-gas compounds. Isoprene may desorbed from the adsorbent using, for example, nitrogen and condensed at low temperature and high pressure.

EXAMPLES Example 1 Enzyme Activity of R-Specific Enoyl-CoA Hydratase Accepting 3-Methyl-3-Hydroxypentanoyl-CoA and 4-Methyl-3-Hydroxypentanoyl-CoA as Substrate

The C-terminal his-tagged phaJ gene (SEQ ID NO: 16) from Aeromonas punctata was cloned into a pE23a expression vector under the T7 promoter. The expression vector was transformed into a BL21[DE3] E. coli host.

The resulting recombinant E. coli strain was cultivated in a 1 L shake flask culture containing 100 mL Luria Broth media at 30° C., shaking at 200 rpm. The culture was induced using 1 mM IPTG for 2 h.

The pellet from each of the induced shake flask cultures was harvested by centrifugation. The pellet was resuspended in 20 mM HEPES (pH=7.2), 1 mM PMSF and 29 U benzonase. The resuspended pellet was lysed via sonication. The cell debris was separated from the supernatant via centrifugation and filtered using a 0.2 μm filter.

The phaJ enzyme was purified from the supernatant using Ni-affinity chromatography and concentrated to 1.25 mg/mL.

The native enzyme activity assay in the forward (hydration) direction was undertaken in a buffer composed of 10 mM ammonium acetate (pH=8) and 1 mM of crotonyl-CoA from Sigma-Aldrich at 30° C. The enzyme activity assay reaction was initiated by adding 0.4 μM of purified enoyl-CoA hydratase to the assay buffer containing the substrate. The enzyme encoded by phaJ accepted crotonyl-CoA as substrate as confirmed via spectrophotometry at 263 nm at 30° C. The substrate only control showed minimal spontaneous hydration of crotonyl-CoA as determined by spectrophotometry at 263 nm. See FIG. 10.

The native enzyme activity assay in the reverse (dehydration) direction was undertaken in a buffer composed of 10 mM ammonium acetate (pH=8) and 1 mM of racemic 3-hydroxybutanoyl-CoA. The enzyme activity assay reaction was initiated by adding 5 μM of purified enoyl-CoA hydratase to the assay buffer containing the substrate and incubated at 30° C. for 1 h. The enzyme encoded by phaJ accepted 3-hydroxybutanoyl-CoA as substrate as confirmed via LC-MS. The substrate only control showed negligible spontaneous dehydration of 3-hydroxybutanoyl-CoA. As demonstrated previously (Lan and Liao, PNAS, 2012, 109(16), 6018-6023), the enoyl-CoA hydratase encoded by phaJ is reversible, though favors the forward (hydration) direction. See FIG. 11.

The non-native enzyme activity assay in the reverse (dehydration) direction was undertaken in a buffer composed of 10 mM ammonium acetate (pH=8) and 1 mM of 3-methyl-3-hydroxypentanoyl-CoA. The enzyme activity assay reaction was initiated by adding 5 μM of purified enoyl-CoA hydratase to the assay buffer containing the substrate and incubated at 30° C. for 1 h. The enzyme encoded by phaJ accepted 3-methyl-3-hydroxypentanoyl-CoA as substrate as confirmed via LC-MS. The substrate only control showed no spontaneous dehydration of 3-methyl-3-hydroxypentanoyl-CoA. See FIG. 12.

The non-native enzyme activity assay in the reverse (dehydration) direction was undertaken in a buffer composed of 10 mM ammonium acetate (pH=8) and 1 mM of 4-methyl-3-hydroxypentanoyl-CoA. The enzyme activity assay reaction was initiated by adding 5 μM of purified enoyl-CoA hydratase to the assay buffer containing the substrate and incubated at 30° C. for 1 h. The enzyme encoded by phaJ accepted 4-methyl-3-hydroxpentanoyl-CoA as substrate as confirmed via LC-MS. The substrate only control showed no spontaneous dehydration of 4-methyl-3-hydroxypentanoyl-CoA. See FIG. 13.

The enoyl-CoA hydratase encoded by phaJ from Aeromonas punctata accepted 3-methyl-3-hydroxypentanoyl-CoA and 4-methyl-3-hydroxypentanoyl-CoA as substrate in the dehydration direction. Given the reversibility of the enzyme reaction and the favoured hydration direction, the enoyl-CoA hydratase encoded by phaJ from Aeromonas punctata accepts 3-methyl-pent-2-enoyl-CoA and 4-methyl-pent-2-enoyl-CoA as substrate.

Example 2 Enzyme Activity of GHMP Superfamily Enzymes, Mevalonate Diphosphate Decarboxylase and Mevalonate-3-Kinase, Accepting 3-Methyl-3-Hydroxypent-4-Enoate as Substrate, Forming Isoprene

Each of the sequences encoding a C-terminal His-tagged gene encoding the mevalonate diphosphate decarboxylase of SEQ ID NOs: 8, 9, 10, and 11 respectively (see FIG. 9) and the mevalonate 3-kinase of SEQ ID NO: 12 (see FIG. 9) was cloned into a PD681-CH expression vector under control of the rhapBAD promoter, such that a C-terminal HIS tagged GHMP superfamily enzyme could be produced. Each expression vector was transformed into a BL21[DE3] E. coli host. The resulting recombinant E. coli strains were cultivated at 37° C. in a 5 L shake flask culture containing 1 L Luria Broth (LB) media and kanamycin antibiotic selection pressure, with shaking at 90 rpm. At an OD₆₀₀ between 0.6 to 0.8, the culture was induced with L-rhamnose to a final concentration of 2 g/L. The cultures was induced for 6 h at 37° C. The pellets from the induced shake flask cultures were harvested via centrifugation and stored at −20° C.

Each frozen pellet was thawed, resuspended and lysed in a lysis buffer containing 50 mM Tris.HCl (pH=8.0), 50 mM NaCl, 1 mM MgCl₂ 1% (w/v) Triton X-100, 1 mg/mL lysozyme and 10 U/mL benzonase for 1 h at 30° C. The cell debris was removed via centrifugation. The GHMP superfamily enzymes were purified from the resulting supernatant using Ni-affinity chromatography and the eluate was buffer exchanged and concentrated via ultrafiltration (10 kDa MWCO) into 100 mM HEPES (pH=7.0), 100 mM KCl to a final enzyme concentration of 200 μM.

Each enzyme activity assay was performed in an assay buffer composed of 100 mM HEPES (pH=7.0), 100 mM KCl, 30 mM MgCl₂, 30 mM ATP, 2 mM DTT and 10 mM of 3-methyl-3-hydroxypent-4-enoate as substrate. Each enzyme activity assay reaction was initiated by adding 0.5 mL of the enzyme stock of SEQ ID NOs: 8, 9, 10, 11 or 12 to 0.5 mL of assay buffer in a 10 mL crimped glass vial and incubating at 30° C. for 24 h. The headspace of each glass vial was analysed by GC-MS for isoprene and compared to the empty vector control. The gene product of SEQ ID NOs: 8, 9, 10, 11 and 12 accepted 3-methyl-3-hydroxypent-4-enoate as substrate as confirmed via GC-MS (see FIG. 14) and synthesized isoprene as reaction product.

Example 3 Enzyme Activity of Linalool Dehydratase Accepting 3-Methyl-3-Buten-2-ol as Substrate, Forming Isoprene

A sequence encoding a C-terminal His-tag encoding the linalool dehydratase of SEQ ID NO: 13 (see FIG. 9) was cloned into a pET15 expression vector under control of the T7 promoter such that a C-terminal HIS tagged enzyme could be produced. The expression vector was transformed into a BL21[DE3] E. coli host. The resulting recombinant E. coli strain was cultivated at 30° C. in a 1 L shake flask culture containing 100 mL Auto-Induction media and antibiotic selection pressure, shaking at 220 rpm overnight. The pellet from the induced shake flask culture was harvested via centrifugation and used immediately in a whole cell assay.

The pellet was washed and resuspended in M9 minimal media to 160 mg/mL (wet weight) and dispensed into 10 mL crimped glass vials in triplicate. The substrate 3-methyl-3-buten-2-ol was added to a final concentration of 20 mM and incubated at 30° C. at 220 rpm for 48 h. The headspace of each glass vial was analysed by GC-MS for isoprene and compared to the empty vector control (undertaken in triplicate). The gene product of SEQ ID NO: 13 accepted 3-methyl-3-buten-2-ol as substrate as confirmed via GC-MS (see FIG. 15) and synthesized isoprene as reaction product.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims. 

What is claimed is:
 1. A method for enzymatically synthesizing isoprene in a recombinant host, said method comprising enzymatically introducing a terminal vinyl group into mevalonate using a dehydratase classified under EC 4.2.1.- where said dehydratase has at least 90% sequence identity to the amino acid sequence set forth in SEQ ID NO: 22 and is capable of converting mevalonate to 3-methyl-3-hydroxy-pent-4-enoate, and converting the resulting 3-methyl-3-hydroxy-pent-4-enoate to isoprene using a linalool dehydratase that has at least 90% sequence identity to the amino acid sequence of SEQ ID NO:
 13. 2. The method of claim 1, where the dehydratase is an oleate hydratase classified under EC 4.2.1.- and has the amino acid sequence set forth in SEQ ID NO:
 22. 3. A method for enzymatically synthesizing isoprene in a recombinant host, according to claim 1, where the said method comprises enzymatically introducing a second terminal vinyl group into 3-methyl-3-hydroxy-pent-4-enoate using a linalool dehydratase that has the amino acid sequence of SEQ ID NO: 13 and is capable of converting the 3-methyl-3-hydroxy-pent-4-enoate to isoprene.
 4. The method of claim 1, where the recombinant host is a prokaryotic host selected from the genus Escherichia such as Escherichia coli; from the genus Clostridia such as Clostridium ljungdahlii, Clostridium autoethanogenum or Clostridium kluyveri; from the genus Corynebacteria such as Corynebacterium glutamicum; from the genus Cupriavidus such as Cupriavidus necator or Cupriavidus metallidurans; from the genus Pseudomonas such as Pseudomonas jluorescens or Pseudomonas putida; from the genus Bacillus such as Bacillus subtillis; or from the genus Rhodococcus such as Rhodococcus equi.
 5. The method of claim 1, where the recombinant host is a eukaryotic host selected from the genus Aspergillus such as Aspergillus niger; from the genus Saccharomyces such as Saccharomyces cerevisiae; from the genus Pichia such as Pichia pastoris; from the genus Yarrowia such as Yarrowia lipolytica, from the genus Issatchenkia such as Issathenkia orientalis; from the genus Debaryomyces such as Debaryomyces hansenii; from the genus Arxula such as Arxula adenoinivorans; or from the genus Kluyveromyces such as Kluyveromyces lactis.
 6. The method of claim 1, wherein a principal carbon source fed to the recombinant host derives from a biological or a non-biological feedstock.
 7. The method of claim 6, wherein the biological feedstock is, or derives from, monosaccharides, disaccharides, hemicellulose such as levulinic acid and furfural, cellulose, lignocellulose, lignin, triglycerides such as glycerol and fatty acids, agricultural waste or municipal waste, or wherein the non-biological feedstock is, or derives from, either natural gas, syngas, CO₂/H₂, methanol, ethanol, non-volatile residue (NVR), caustic wash from cyclohexane oxidation processes or other waste stream from either the chemical or petrochemical industries.
 8. The method of claim 1, wherein said host comprises a feedback inhibition resistant mutant of an acetolactate synthase.
 9. The method of claim 1, wherein said host comprises an acetolactate synthase under control of a promoter not subject to genetic repression by a branched chain amino acid. 